Document DMZawryoZDOOpq0RNJBeEQ73B

American Society of Heating and Ventilating Engineers Guide, 1935~ can be fired at least 16 in. deep. The air spaces between the pieces of coal are large, and for best results this coal should be fired deeply. Stove size coal is the proper size of anthracite for many boilers and furnaces used for heating buildings. It burns well on grates at least 16 in. in diameter and 12 in. deep. The only instructions needed for burning this type of fuel are that the grate should be shaken daily, the fire should never be poked, or disturbed, and the. fuel should be fired deeply and uniformly. Chestnut size coal is in demand for firepots up to 20 in. in diameter, with a depth of from 10 to, 15 in. Pea size coal is often ah economical fuel to burn. It is relatively low in price. When fired carefully, pea coal can be burned on standard grates. It is. well to have a small amount of a larger fuel on hand when building new fires, or when filling holes in the-fuel- bed. Care should be taken to shake the grates only until the first bright coals begin to fall through the grates. The fuel bed, after a new fire has been built, should be increased in thickness by the addition of small charges until it is at least level with the sill of the fire door. This keeps a bed of ignited coal in readiness against the time when a sudden demand for heat shall be made on the heaPteear. size coal requires a strong draft and therefore the best results generally will be obtained by- keeping the choke damper open, the coldair check closed, and by controlling the fire with the air-inlet damper only. Pea size can also be fired in layers with stove or egg size anthracite and its use in this manner will reduce the fuel costs and attention required. Buckwheat size coal requires much the same attention as pea size coal, except that the smaller size of the fuel makes it more difficult to burn on ordinary grates. Even greater care must be taken in shaking the grates than with pea coal on account of the danger of the fuel falling through the grate. A good draft is required and consequently the fire is best controlled by the air-inlet damper only. Where frequent attention can be given and where there is not a big heat-demand, this fuel is frequently burned without the aid of any special equipment. In general it will be found more satisfactory with buckwheat coal to maintain a uniform heat output and consequently to keep the system warm all the time, rather than to allow the system to cool off at times and then to attempt to bum the fuel at a high rate while warming up. A uniform low fire will minimize the clinker formation and keep the clinker in an easily broken up condition so that it readily can be shaken through theFogrrcaeted. draft and special grates or retorts frequently are used with this fuel for best results. No. 2 buckwheat anthracite, or rice size, is used only with forced draft equipment on mechanical stokers. No. 3 buckwheat anthracite, or barley, has no application in domestic heating. Firing Bituminous Coal Bituminous coal should never be fired over the entire fuel bed at one time. A portion of the glowing fuel should always be left exposed to ignite the gases leaving the fresh charge. Chapter 27 Fuels and Combustion- Air should be admitted over the fire through a special secondary air device, or through a slide in the fire door or by opening the fire door slightly. If the quantity of air admitted is too great the gases will be cooled below the ignition temperature and will fail to burn. The fireman can judge the quantity of air to admit by noting when the air supplied is just sufficient to make the gases burn rapidly and smokelessly above the fuel bed. The red fuel in the firebox, before firing, excepting only a shallow layer of coke on the grate, should be pushed to one side or forward or back-' ward to form a~ hollow in which'to throw the fresh fuel. Some manu facturers recommend that all red fuel be pushed to the rear of the firebox and that the fresh fuel be fired directly on the grate and allowed to ignite from the top. The object of this is to reduce the early rapid distillation of gases and to reduce the quantity of secondary air required for smoke less combustion. It is well to have the bright fuel in the firebox so placed that the gases from the freshly fired fuel, mixed with the air over the fuel bed, pass over the bed of bright fuel on the way to the flues. The bed of bright fuel then supplies the heat to raise the mixture of air and gas to the ignition temperature, thereby causing the gaseous matter to burn and preventing the formation of smoke. The fuel bed should be carried as deep as the size of fuel and the available draft permit, in order to have as much coked fuel as possible for pushing to the rear of the firebox at the time of firing. A deep fuel bed allows the longest firing intervals. If the coal is of the caking kind the fresh charge will fuse into one solid mass which can be broken up with the stoking bar and leveled from 20 min to one hour after firing, depending on the temperature of the firebox. Care should be exercised when stoking not to bring the bar up to the-surface of the fuel as this will tend to bring ash into the high temperature zone at the top of the fire, where it will melt and form clinker. The stoking bar should be kept as near the grate as possible and should be raised only enough to break up the fuel. With fuels requir ing stoking it may not.be necessary to shake the grates,-as the ash is usually dislodged during stoking. The output obtained from any heater with bituminous coal will usually exceed that obtainable with anthracite, since soft coal burns more rapidly than hard coal and with less draft. Soft coal, however, will require frequent attention to the fuel bed, because it burns unevenly, even though the fuel bed may be level, forming holes in the fire which admit too much air, chilling the gases over the fuel bed and reducing the available draft. Semi-bituminous coal is fired as bituminous coal, and because of its caking characteristics it requires practically the same attention. The Pocahontas Operators Association recommends the central cone method of firing, in which the coal is heaped on to the center of the bed forming a ?ne the top of which should be level with the middle of the firing door. This allows the larger lumps to fall to the sides; and the fines,to remain in jse center and be coked. The poking should be limited to breaking down the coke without stirring, and to gently rocking the grates. It is recom- c' 449